Characterisation of structural and surface speciation of representative commercially available cerium oxide nanoparticles

The shape, morphology, crystallography, and oxidation state of commercially available cerium oxide nanoparticles as compared with bulk particles were studied by high-resolution transmission electron microscopy coupled to electron energy loss spectroscopy, along with scanning electron microscopy. Nano and bulk particles have the same crystalline structure and morphology as the fluorite-type structure with a mainly octahedral shape enclosed by eight {111} facets, or a truncated octahedral shape enclosed by eight {111} facets and two {002} facets, or eight {111} and two {002} and four {220} facets. Some defects, including twin boundaries and steps and kinks, were observed. Bulk ceria particles contain mainly Ce(IV), whereas ceria nanoparticles contain a large fraction of Ce(III), which decreases after interaction with humic acid and biological media. These properties are likely to play an essential role in the environmental and toxicological behaviour of nanoparticles.